The present invention relates to a multi cylinder internal combustion engine comprising a cylinder head internally defining exhaust passages and upper and lower water jackets above and below the exhaust passages.
A multi cylinder internal combustion engine comprising a cylinder head internally defining exhaust passages and upper and lower water jackets above and below the exhaust passages was proposed in Japanese patent laid open publication No. 2000-161132 in the name of the assignee of this application. In this proposal, the axial lines of the exhaust passages extended substantially perpendicularly to the axial cylinder axial lines to minimize the vertical dimension of the cylinder head.
However, the greater the output of an internal combustion engine is or the larger the displacement of an internal combustion engine is, the more stringent is the cooling requirement of the engine becomes. Therefore, the prior proposal was found to be inadequate to meet the need of more powerful, larger internal combustion engines.
Furthermore, according to the prior proposal, the communication passages communicating the upper and lower water jackets with each other were each provided between the exhaust ports of the corresponding cylinder, and there was a serious difficulty in enlarging these passages. Therefore, the communication passages created a large resistance to the cooling water flow. Also, when casting the cylinder head, the core parts for forming the upper and lower water jackets are supported by the core parts for forming the communication passages, and the limited size of the communication passages prevented an adequate mechanical strength from being provided to the core parts.
In view of such problems of the prior art, a primary object of the present invention is to provide a multi cylinder internal combustion engine having a compact exhaust manifold arrangement internally defined in a cylinder head which is provided with a favorable cooling water jacket arrangement.
A second object of the present invention is to provide a multi cylinder internal combustion engine having a compact exhaust manifold arrangement internally defined in a cylinder head which can be fabricated by casting in a favorable manner.
According to the present invention, these and other objects can be accomplished by providing a multi cylinder internal combustion engine comprising a cylinder head internally defining exhaust passages extending from a plurality of combustion chambers defined in part by the cylinder head, the exhaust passages converging into a converging area also internally defined in the cylinder head, wherein: an upper water jacket and a lower water jacket are formed above and below the exhaust passages, and the lower water jacket has a greater volume than the upper water jacket.
Thus, the cooling efficiency for the converging area can be improved by increasing the volume of the part of the water jacket adjacent to the converging area. Also, because the upper water jacket has a relatively small volume, the load on the core parts supporting the core part for defining the upper water jacket can be reduced, and the overall mechanical strength of the core can be improved. By extending the water jackets to the converging area, the cooling efficiency can be improved even further.
According to a preferred embodiment of the present invention, the converging area and the exhaust passages are defined at least in part by an exhaust passage wall extending laterally from the cylinder head defining an arched profile in a plane perpendicular to a cylinder axial line, and an upper water jacket and a lower water jacket are formed above and below the converging area, laterally outer walls of the upper and lower water jackets extending adjacent to the exhaust passage wall with a thick walled portion formed between the exhaust passage wall and at least one of the laterally outer walls of the upper and lower water jackets. Preferably, an exhaust outlet communicating with the converging area is formed centrally in the exhaust passage wall, and the thick walled portion is connected to a mounting surface defined around the exhaust outlet for joining an exhaust system.
If a communication passage communicating the upper and lower water jackets with each other is formed between exhaust passages extending from adjacent cylinders, the mechanical strength of the core parts joining those for defining the upper and lower water jackets can be increased, and this contributes to the increase in the overall mechanical strength of the core of the die assembly for casting the cylinder head.
An oil passage may also be internally defined in the cylinder head so that at least a part of the water jackets surrounds the oil passage. This oil passage may be formed in a vertical wall formed internally in the cylinder head between adjacent combustion chambers. Preferably, the oil passage and the communication passage may be formed commonly in the same vertical wall.